The invention pertains to apparatuses and methods for microwave vacuum-drying of organic materials, such as food products.
Dehydration of organic materials is commonly done in the food processing industry and in the production of biologically-active materials. It may be done in order to preserve the products for storage, or to create a product that is used in the dehydrated form, for example dried herbs and various kinds of chips. One method employed to dehydrate food products and biologically-active materials is microwave vacuum dehydration. Examples of this in the patent literature include U.S. Pat. No. 6,442,866, Wefers; WO 2009/049409, Durance et al.; WO 2009/033285, Durance et al.; and WO 2011/085467, Fu et al. Microwave vacuum-drying is a rapid method that can yield products with improved quality compared to air-dried and freeze-dried products. Because the drying is done under reduced pressure, the boiling point of water and the oxygen content of the atmosphere are lowered, so food and medicinal components sensitive to oxidation and thermal degradation can be retained to a higher degree than by air-drying. The drying process is also much faster than air- and freeze-drying. However, in some prior art microwave-vacuum driers, substantial disassembly of the apparatus is required to provide access to the interior of the vacuum chamber for purposes of cleaning and repair. In others, relatively high power microwave generators are required, which are expensive and increase the risk of microwave arcing within the vacuum chamber, and thus limit the range of pressures at which the chamber can be operated.